1. Technical Field
This invention relates generally to dynamic shaft seals and more particularly to those employing a wear sleeve.
2. Related Prior Art
Shaft seals are used in engine applications and the like for sealing a bore or opening in a housing through which a rotatable shaft extends to prevent the leakage of lubricant and the ingress of contaminants. The typical shaft seal includes an outer annular metal carrier fixed to the housing. An annular seal member is fixed to the carrier and is formed with at least one inner annular seal lip encircling the shaft. In some applications, the seal lip runs directly on the outer surface of the shaft, whereas in other applications the lip runs on a metal wear sleeve disposed about and rotatable with the shaft. The wear sleeve provides a hard, smooth contact surface that is the same for all such seals independent of the condition of the shaft on which it is installed.
Wear sleeves are typically press-fitted onto the shaft in order to provide sufficient interference to secure the sleeve against movement on the shaft and to provide intimate metal-to-metal contact between the sleeve and the shaft to facilitate rapid dissipation of heat away from the seal member to protect the lip against premature wear or damage or material degradation or coking of the lubricant from exposure to excessive heat. The press-fit interference is achieved by closely matching the inner surface diameter of the sleeve to that of the outer surface of the shaft, such that when the sleeve is pressed onto the shaft, tight metal-to-metal press-fit engagement is provided therebetween.
One disadvantage of using such sleeves is that high installation forces are required for press-fitting the sleeve onto the shaft. The high force pressing operation requires special equipment and adds time and cost to the installation of seal assemblies. Moreover, press-fit seals are inherently difficult to remove once installed, since the press-fit engagement must be overcome. Special care must also be taken to avoid damaging the shaft and other components during removal of the press-fit sleeve.
U.S. Pat. No. 5,082,294, which is commonly owned by the assignee of the present invention and its disclosure incorporated herein by reference, discusses some alternatives to press-fit wear sleeves and proposes still others. An intermediate elastomeric liner is disposed between the wear sleeve and shaft to fix the wear sleeve against rotation on the shaft during service without the need for a press-fit connection. However, in applications where high heat transfer is needed, the elastic liner may present an undesirable barrier to the flow of heat from the wear sleeve to the shaft and thus may impair heat dissipation. An alternative solution proposed by the '294 patent is the provision of a deformable metallic liner that is squeezed with a press-fit between the wear sleeve and shaft to achieve the desired metal-to-metal contact for efficient conduction of heat away from the sealing lip. However, such an arrangement adds a component and steps to the installation process and does not overcome the problems associated with removing press-fitted wear sleeves.
Accordingly, there is a need in the industry for a wear sleeve that installs on the shaft with low insertion force and achieves intimate metal-to-metal contact with the shaft once installed, yet is removable from the shaft with low force to facilitate easy replacement of the seal assembly, and particularly the wear sleeve.